3-D Hybrid Beamforming Based on Time Delay Compensation Network

The terahertz (THz) band offers significantly higher bandwidth compared to the millimeter-wave (mmWave) band. However, as the operating frequency increases, the severe attenuation of THz signals poses substantial challenges. To address this issue, ultra-massive multiple-input multiple-output (UM-MIMO) technology is employed to provide enhanced beamforming gain and spectral efficiency. Nevertheless, the severe beam splitting effect in wideband THz systems degrades array gain and overall system performance. Utilizing true time delay (TTD) to introduce frequency-dependent phase shifts has proven to be an effective solution for mitigating the beam splitting effect. However, due to the high cost of TTDs, existing studies often adopt partially connected structures, where each TTD is connected to multiple antenna elements through phase shifters (PS). This paper investigates the beam splitting effect in uniform planar arrays (UPA) and analyzes issues such as energy leakage and carrier gain reduction in TTD partially connected structures. A novel TTD connection architecture is proposed to address these challenges. Simulation results demonstrate that the proposed structure achieves performance comparable to the fully connected TTD architecture while significantly reducing the required number of TTDs, with performance approaching that of fully digital beamforming.